1. Field of the Invention
The present invention relates to an optical communication module for use in optical communications as a transmitter or a receiver. More particularly, it relates to a configuration of an optical communication module capable of extending a frequency band to further improve a communication rate and of elevating an S/N ratio to improve a communication quality in the optical communication module.
2. Description of the Related Art
In a conventional optical communication module, a light-emitter and a photodetector may be mounted on a substrate. For example, the light-emitter and the photodetector are mounted on one surface of a multi-layered printed-circuit board, and signal processing ICs for the light-emitter and the photodetector are mounted on the rear surface of the same multi-layered printed-circuit board. (For example, see Japanese Patent Application Laid-Open No. 2002-296435, paragraphs 0021-0078, FIG. 1).
If the light-emitter and the photodetector are mounted on the printed circuit board so as to project from the surface of the board, a light emitted from the light-emitter may easily reach around to the photodetector, causing so-called crosstalk, which lowers the S/N ratio and deteriorates the communication quality disadvantageously. In order to prevent the communication quality from such deteriorating, a half-duplex system is required because it is not operative to receive during the light-emitting element is driven to transmit. This system, however, results in extreme loss of convenience.
An excellent high frequency characteristic can not be expected from the printed circuit board that includes the light-emitter, the photodetector and their associated circuits mounted thereon. In addition, such the board has a limit in high-speed signaling. Therefore, even if high-speed elements of light-emitter and photodetector are applied for transmitting and receiving, their effect can not be exhibited sufficiently. Consequently, the communication rate of the optical communication module suffers some constraint about the characteristic of the printed circuit board.